The invention relates to a device for withdrawing a liquid from a container according to the preamble of claim 1. Here, devices for needle-free withdrawal of pharmaceutical substances from a hermetically sealed glass vessel are generally concerned. Here, the liquid can be transferred into an injection syringe, wherein the needle is only fitted subsequently. Of course, devices of this type can also be used in the non-medical field however, for example for chemical analysis purposes in the food processing field, etc.
A generically comparable device is known by WO 01/60436, in which a linearly displaceable piercing tip is held in a tubular housing, which is fitted onto the closed container mouth. The piercing tip is fixed in the above idle position by flexible detent catches and has a circumferential toothing, which engages in corresponding lateral tooth segments. In the event of application of a pressure from above in the direction of the container once a syringe has been attached, the piercing tip releases from the latched connection and slides downwardly in the toothing in a manner fixed against rotation until the sealing plug on the container has been pierced. The container content can then be aspirated by means of the injection syringe.
A significant disadvantage of known devices lies in the fact that, even once the sealing element has been pierced by the hollow needle, the interior of the container is sealed with respect to the atmosphere when another container, such as an injection syringe, is attached to the penetration element. As the liquid is aspirated from the container, a negative pressure is thus produced, which in extreme cases causes the majority of the liquid to flow back into the container as soon as the pump movement is interrupted. Due to the flexibility of the sealing element, air may flow along the outer face of the hollow needle with a strong negative pressure in the container. This is undesirable however because microbiological impurities can thus infiltrate the container and therefore the liquid.